In the aeronautical field, many aircraft components are made of composite material in order to reduce the onboard mass and thereby the energy consumption of the aircraft. By way of example, the orbital frames of the fuselage, the stringers and the fuselage panels may be made of composite material.
Some of these composite components need to be machined in order to create, amongst other things, through-holes which are used notably for joining the components together.
A first approach, illustrated in FIG. 1, might be to make a through-hole 10 in a component 12 by drilling, using a drill bit 14 secured to a tool holder 16 which pivots about a rotation axis 18 with respect to a machine tool 20. With this approach, the axis 22 of the drill bit 14 coincides with the axis of rotation 18 and machining is the result of the combination of a rotational movement of the drill bit 14 about its axis 22 and of a tool feed movement of the drill bit advancing in a direction parallel to the axis 22.
During drilling, as long as the central point 24 of the end of the drill bit 14 has not come through, the drill bit 14 exerts on the component 12 axial loads (along the axis 22) that are high because the speed of the central point 24 in a plane perpendicular to the axis 22 is zero. These axial loads cancel as soon as the central point 24 comes through.
When the drilling is being done in a thin wall of the component 12 which may deform elastically because of the axial loads, it is necessary to provide a tool 26 of the sheet clamp type in order to ensure the transfer of the axial loads and limit the deformations of the component. This tool 26 comes into contact, as close as possible to the edge of the through-hole 10, with the surface 28 of the component 12 that is on the opposite side to the surface 30 via which the drill bit 14 enters.
During drilling, this tool 26:    makes it possible to prevent the deformation of the component in bending in a way likely to cause the hole to be geometrically non-compliant,    makes it possible to prevent component spring-back as the drill bit comes through, which spring-back is likely to cause delaminating and flaking around the edge of the hole in the case of a composite material.
The use of a tool 26 of the sheet clamp type is not entirely satisfactory because the movements of the parts located on each side of the component need to be coordinated and these parts need to be positioned correctly relative to one another, all of which tends to make tool movement management more complicated.
For certain components, given their geometries, it may prove to be impossible to position a tool on the opposite surface 28 to the surface 30 via which the drill bit 14 enters.
Another approach, illustrated in FIG. 2, might be to create a through-hole 10′ in a component 12′ using the orbital drilling technique.
In that case, a shell end-mill milling cutter 32 is used, this being secured to an electric spindle 34 which rotates the milling cutter 32 about a first rotation axis 36. The electric spindle 34 is secured to a machine tool 38 which rotates it about a second rotation axis 40. The first rotation axis 36 is parallel to and eccentric with respect to the second rotation axis 40. Thus, the diameter of the through-hole 10′ is dependent on the diameter of the milling cutter 32 and on the eccentricity E between the two rotation axes 36 and 40.
With this approach, the electric spindle 34 rotates the milling cutter 32 at the high rotational speeds used in High-Speed Machining HSM. The machine tool 38 performs the tool feed movement in the direction of the axis 40 and the orbital movement of the first rotation axis 36.
This second approach does not require the use of a tool of the sheet clamp type, because the axial loadings are lower because there is no point on the end of the milling cutter that has zero speed in a plane perpendicular to the axis 36.
However, this second approach is not entirely satisfactory because of its low productivity.
This is because the eccentricity between the two axes 36 and 40 needs to be adjustable so that the diameter of the through-hole can be adjusted, and because of this, the electric spindle 34 cannot be balanced. As a result, its rotational speed about the second rotation axis needs to be low (200 rpm at most) in order to limit the onset of vibration phenomena.